Message-ID: <20070302071423.GA30634@elte.hu>
Date:	Fri, 2 Mar 2007 08:14:23 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Jens Axboe <jens.axboe@...cle.com>, Pavel Machek <pavel@....cz>,
	Adrian Bunk <bunk@...sta.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Michael S. Tsirkin" <mst@...lanox.co.il>,
	Thomas Gleixner <tglx@...utronix.de>, linux-pm@...ts.osdl.org,
	Michal Piotrowski <michal.k.k.piotrowski@...il.com>,
	Daniel Walker <dwalker@...sta.com>
Subject: Re: 2.6.21-rc1: known regressions (part 2)


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> Btw, you seem to have re-ordered the commits - the above is not the 
> order you did the bisection in. The known-good commit (f3ccb06..) is 
> in the middle. [...]

no - i simply picked them by hand, based on looking at gittk output, 
because bisection did not appear to find anything useful:

  9f4bd5dde81b5cb94e4f52f2f05825aa0422f1ff is first bad commit

And via that method i found a couple of more 'good' points - which 
git-bisect never picked up by itself. (and i did 3-4 separate git-bisect 
sessions, one of them was a "git-bisect start drivers/acpi/" - which is 
the main area of suspicion). I looked at git-bisect visualize more than 
once, and i've attached one of the bisection logs below.

i also think i know what happens. Firstly, my testing is reliable, as i 
mentioned it in the other mail i frequently re-visited commits to make 
sure that none of my bad/good decisions is spurios - but no, the test 
results are extremely reproducable: either the laptop resumes properly 
after flashing its disk light or it does not.

the problem i think is that i simply took git-bisect's behavior for 
granted (i used it many times already) but forgot about a very basic 
precondition: git-bisect will find only a /single/ good->bad transition.

If there is a bad->good transition combined with a good->bad transition 
then git-bisect will think it's the same 'badness', while it's a 
/former/ badness that it is honing in on - totally sending the bisection 
off into la-la-land.

so as i mentioned it in the first mail: i /know/ that this commit is a 
bad->good transition point:

  f3ccb06f3b8e0cf42b579db21f3ca7f17fcc3f38

/and i only want to test commits that include this commit/ - because i 
know that without this commit git-bisect confuses the /other/ breakage 
with the new breakage. In the bisection log below, this choice of 
git-bisect:

  ee404566f97f9254433399fbbcfa05390c7c55f7

is 'bad' according to testing, but that's 'another' badness - and i 
missed it.

Now, having slept on it, the solution is very simple: whenever 
git-bisect picks a commit for which the following command comes up 
empty:
 
  git-log | grep f3ccb06f3b8e0cf42b579db21f3ca7f17fcc3f38

then i'll mark it "git-bisect good" - artificially marking the older 
badness as a 'good' area. That way git-bisect will find the right 
good->bad transition point.

btw., that's why i tried to pick up commits by hand, making sure that 
commit f3ccb06f3b8e0cf42b579db21f3ca7f17fcc3f38 is always included - but 
got lost in the maze of the commit graph, and didnt realize that there 
is a simple solution. Nevertheless i wanted to dump the information i 
already gathered. Those commits were totally out of order, etc. - they 
were picked by a poor human who is much worse at walking graphs than 
git-bisect ;-)

	Ingo

git-bisect start
# bad: [01363220f5d23ef68276db8974e46a502e43d01d] [PARISC] clocksource: Move update_cr16_clocksource later in boot
git-bisect bad 01363220f5d23ef68276db8974e46a502e43d01d
# good: [f3ccb06f3b8e0cf42b579db21f3ca7f17fcc3f38] ACPI: Disable wake GPEs only once.
git-bisect good f3ccb06f3b8e0cf42b579db21f3ca7f17fcc3f38
# bad: [ee404566f97f9254433399fbbcfa05390c7c55f7] sysctl: mips/au1000: remove sys_sysctl support
git-bisect bad ee404566f97f9254433399fbbcfa05390c7c55f7
# bad: [c827ba4cb49a30ce581201fd0ba2be77cde412c7] Merge master.kernel.org:/pub/scm/linux/kernel/git/davem/sparc-2.6
git-bisect bad c827ba4cb49a30ce581201fd0ba2be77cde412c7
# bad: [68a696a01f482859a9fe937249e8b3d44252b610] Merge branch 'upstream' of git://ftp.linux-mips.org/pub/scm/upstream-tc
git-bisect bad 68a696a01f482859a9fe937249e8b3d44252b610
# bad: [1c433fbda4896a6455d97b66a4f2646cbdd52a8c] [ALSA] soc - 0.13 ASoC headers
git-bisect bad 1c433fbda4896a6455d97b66a4f2646cbdd52a8c
# bad: [048b945077bdc7e8dff5d5810ff2a0ced3590ca9] [ALSA] echoaudio, add TLV support
git-bisect bad 048b945077bdc7e8dff5d5810ff2a0ced3590ca9
# bad: [c07584c83287ae5a13cc836f69a1d824ad068c66] [ALSA] hda-codec - Add support for Medion laptops
git-bisect bad c07584c83287ae5a13cc836f69a1d824ad068c66
# bad: [dbc6b6ad767c86907db373e85139b0e975ba7599] [ALSA] ASoC codecs: generic AC97 support
git-bisect bad dbc6b6ad767c86907db373e85139b0e975ba7599
# bad: [b66b3cfe6c2f6560f351278883a325b6ebc478f5] [ALSA] hda_intel: increase maximum DMA buffer size to 1024MB
git-bisect bad b66b3cfe6c2f6560f351278883a325b6ebc478f5
# bad: [12b131c4cf3eb1dc8a60082a434b7b100774c2e7] [ALSA] allow registering an alsa device with struct device pointer
git-bisect bad 12b131c4cf3eb1dc8a60082a434b7b100774c2e7
# bad: [e4f8e656d8c152c08cd44d0e3c21f009fab09952] [ALSA] usb-audio: allow pausing
git-bisect bad e4f8e656d8c152c08cd44d0e3c21f009fab09952
# bad: [1700f3080d98323e91864d67cb9f6d46f818ccf0] [ALSA] usb-audio: merge playback/capture hardware information structs
git-bisect bad 1700f3080d98323e91864d67cb9f6d46f818ccf0
# bad: [9f4bd5dde81b5cb94e4f52f2f05825aa0422f1ff] [ALSA] snd-emu10k1: Added support for emu1010, including E-Mu 1212m and E-Mu 1820m
git-bisect bad 9f4bd5dde81b5cb94e4f52f2f05825aa0422f1ff
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